DDD is a front-end to a command-line debugger (called inferior debugger, because it lies at the layer beneath DDD).
DDD supports inferior debuggers like GDB, DBX, WDB, Ladebug, JDB, XDB, the Perl debugger, the bash debugger bashdb, the GNU Make debugger remake, or the Python debugger pydb.
Besides ``usual'' front-end features such as viewing source texts, DDD has become famous through its interactive graphical data display, where data structures are displayed as graphs.